U.S. patent number 5,543,250 [Application Number 08/327,838] was granted by the patent office on 1996-08-06 for electrode for storage battery and method for producing the same.
This patent grant is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Takayuki Hayashi, Hiroshi Kawano, Masato Tsuji, Nobuyuki Yanagihara.
United States Patent |
5,543,250 |
Yanagihara , et al. |
August 6, 1996 |
Electrode for storage battery and method for producing the same
Abstract
The electrode comprises a metal substrate and a coated layer of
an active material provided on one or both faces of the substrate.
The metal substrate is a metal sheet having a plurality of punched
holes. The punched holes have burrs along their peripheries so that
the apparent thickness including the burrs is at least twice the
original thickness of the metal sheet. The burrs improve the
engagement between the metal substrate and the coated layer.
Inventors: |
Yanagihara; Nobuyuki (Hirakata,
JP), Kawano; Hiroshi (Ibaraki, JP),
Hayashi; Takayuki (Kadoma, JP), Tsuji; Masato
(Kyoto, JP) |
Assignee: |
Matsushita Electric Industrial Co.,
Ltd. (Kadoma, JP)
|
Family
ID: |
17506538 |
Appl.
No.: |
08/327,838 |
Filed: |
October 27, 1994 |
Foreign Application Priority Data
|
|
|
|
|
Oct 29, 1993 [JP] |
|
|
5-271906 |
|
Current U.S.
Class: |
429/241; 29/2;
29/623.5; 427/126.3 |
Current CPC
Class: |
H01M
4/70 (20130101); Y10T 29/10 (20150115); Y10T
29/49115 (20150115); Y02E 60/10 (20130101) |
Current International
Class: |
H01M
4/70 (20060101); H01M 004/70 () |
Field of
Search: |
;429/241 ;29/2,623.5
;427/126.3,388.1,388.4,376.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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359732 |
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Apr 1906 |
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FR |
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429054 |
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Sep 1911 |
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FR |
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889184 |
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Jan 1944 |
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FR |
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49-77142 |
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Jul 1974 |
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JP |
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58-41975 |
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Mar 1983 |
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JP |
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58-163157 |
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Sep 1983 |
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JP |
|
0212318 |
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Mar 1987 |
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JP |
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1302668 |
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Dec 1989 |
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JP |
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6-76826 |
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Mar 1994 |
|
JP |
|
Primary Examiner: Kalafut; Stephen
Attorney, Agent or Firm: Cushman Darby & Cushman
L.L.P.
Claims
What is claimed is:
1. An electrode for an alkaline storage battery, comprising:
a metal substrate of alkali-resistant metal having two opposite
faces; and
a coated layer including an active material and provided on at
least one face of said metal substrate;
said metal substrate being a metal sheet having a plurality of
holes punched therethrough so as to have ragged-edge punching burrs
extending from at least one face of said metal sheet, along the
periphery of each punched hole;
the thickness of said metal sheet including said punching burrs is
at least twice as large as the thickness of said metal sheet
excluding said punching burrs, said thickness of said metal sheet
excluding said punching burrs being in the range of from 25 .mu.m
to 100 .mu.m.
2. An electrode for an alkaline storage battery in accordance with
claim 1, wherein said punched holes are circular and each punched
hole has a diameter in a range of from 0.2 mm to 2 mm.
3. An electrode for an alkaline storage battery in accordance with
claim 1, wherein said punched holes are rectangular and each side
of each punched hole has a length in a range of from 0.2 mm to 2
mm.
4. An electrode for an alkaline storage battery, comprising a metal
substrate of alkali-resistant metal having two opposite face;
and
a coated layer including an active material and provided on both
faces of said metal substrate
said metal substrate being a metal sheet having a plurality of
holes punched therethrough so as to have ragged edge punching burrs
extending from both faces of said metal sheet, along the
peripheries of said punched holes;
the thickness of said metal sheet including said punching burrs
being least twice the thickness of said metal sheet excluding said
punching burrs, said thickness of said metal sheet excluding said
punching burrs being in the range of from 25 .mu.m to 100
.mu.m.
5. An electrode for an alkaline storage battery in accordance with
claim 4, wherein adjacent punched holes of said metal sheet have
punching burrs on opposite faces of said metal sheet.
6. An electrode for an alkaline storage battery in accordance with
claim 4, wherein said punched holes are circular and each punched
hole has a diameter of from 0.2 mm to 2 mm.
7. An electrode for an alkaline storage battery in accordance with
claim 4, wherein said punched holes are rectangular and each side
of each punched hole has a length of from 0.2 mm to 2 mm.
8. An electrode for an alkaline storage battery, comprising:
first and second metal layers of alkali-resistant metal each having
two faces, each metal layer having a plurality of holes punched
therethrough so as to have ragged edge punching burrs extending
from at least one said face of each said metal layer, along the
peripheries of said punched holes;
the thickness of each metal layer including respective said
punching burrs through the respective said metal layer being at
least twice as large as the thickness of the respective said metal
layer excluding the respective said punching burrs, each said layer
having a thickness, excluding the respective said punching burrs in
the range of from 25 .mu.m to 100 .mu.m; and
a filling of an active material provided between said first and
second metal layers, so as to embed respective of said punching
burrs in said active material.
9. An electrode for an alkaline storage battery in accordance with
claim 8, wherein said first and second metal layers comprise a
folded metal sheet, and said filling comprises a double thickness
of a coated layer of said active material provided on the inwardly
facing face of said folded metal sheet.
10. An electrode for an alkaline storage battery in accordance with
claim 9, wherein said punched holes are circular and each punched
hole has a diameter in a range of from 0.2 mm to 2 mm.
11. An electrode for an alkaline storage battery in accordance with
claim 9, wherein said punched holes are rectangular and each side
of each punched hole has a length in a range of from 0.2 mm to 2
mm.
12. A method for producing an electrode for an alkaline storage
battery, comprising the steps of:
punching a plurality of holes in a metal sheet of alkali-resistant
metal which is from 25 .mu.m to 100 .mu.m thick, so as to produce a
plurality of ranged edge punching burrs extending from at least one
face of said metal sheet, along the peripheries of said punched
holes, and so as to provide said metal sheet with a thickness,
including said punching burrs, which is at least twice the
thickness of said metal sheet excluding said punching burrs;
producing a coated substrate by coating a paste containing an
active material on both faces of said metal sheet, said coated
substrate having a thickness of one to 1.5 times said thickness
including said punching burrs; and
drying said coated substrate and compressing said coated substrate
in the direction of the thickness thereof.
13. A method in accordance with claim 12, wherein said punched
holes are circular and each punched hole has a diameter in a range
of from 0.2 mm to 2 mm.
14. A method in accordance with claim 12, wherein said punched
holes are rectangular and each side of each punched hole has a
length in a range of from 0.2 mm to 2 mm.
15. A method for producing an electrode for an alkaline storage
battery, comprising the steps of:
punching a plurality of holes in a metal sheet of alkali-resistant
metal which is from 25 .mu.m to 100 .mu.m thick so as to produce a
plurality of ragged edges punching burrs extending from one face of
said metal sheet, along the peripheries of said punched holes, and
so as to provide said metal sheet with a thickness, including said
punching burrs, which is at least twice the thickness of said metal
sheet excluding said punching burrs;
producing a coated substrate by coating a paste containing an
active material on said one face of said metal sheet, said coated
substrate having a thickness of one to 1.5 times said thickness
including said punching burrs;
drying said coated substrate;
folding said coated substrate with said coated face being folded
inwards; and
compressing said coated substrate.
16. A method in accordance with claim 15, wherein said punched
holes are circular and each punched hole has a diameter in a range
of from 0.2 mm to 2 mm.
17. A method in accordance with claim 15, wherein said punched
holes are rectangular and each side of each punched hole has a
length in a range of from 0.2 mm to 2 mm.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a storage battery and, more
particularly, to an electrode used for an alkaline storage battery
and a method for producing the same.
2. Description of the Prior Art
A typical positive electrode of an alkaline storage battery is a
nickel electrode. This electrode may be a sintered type electrode
or a non-sintered type electrode. In producing the former type of
electrode, a microporous sintered plaque obtained by sintering
nickel powder is impregnated with an aqueous solution of nickel
nitrate or the like thereby to add nickel salt, and, after drying,
the sintered plaque is immersed in caustic alkali aqueous solution
to convert the nickel salt to nickel hydroxide. This method has the
disadvantage that the process is complicated and the filling
density of nickel hydroxide as an active material is reduced in
comparison with the non-sintered electrode described later. In
spite of this disadvantage, this electrode has a highly efficient
discharge characteristic and a long cycle life, and finds wide
application in a variety of fields.
A non-sintered electrode has previously been of a pocket type.
According to a method recently put into practice, on the other
hand, nickel hydroxide powder as a powder of active material
directly fills a foamed-nickel porous material. This method is a
simple method of electrode production. Further, the availability of
a foamed nickel porous material of high porosity makes it possible
to fill it with nickel hydroxide to a high density and therefore a
high-capacity battery can be produced. The foamed nickel porous
material, however, needs to be produced by electroplating and
therefore has the disadvantage of high material cost.
In view of this, a non-sintered electrode is under development
using a low-cost punched metal or expanded metal in place of the
foamed nickel porous material as an electrode support. These
electrode supports have no three-dimensional structure unlike the
sintered plaque or the foamed-nickel porous material. As a result,
an electrode made of these electrode supports has a low ability to
hold an active material and the active material is liable to fall
off during electrode fabrication or repeated charging and
discharging. Further, due to the low electronic conductivity in the
electrode thickness direction and a poor electrode characteristic,
these electrode supports find no practical applications except for
special types of electrodes.
The above-mentioned method of electrode production using a punched
metal or expanded metal as an electrode support has the advantage
that a powder of the active material made into a paste with a
solution of a high polymer binder and a conductive powder is coated
and dried on the electrode support and thus the electrode can be
easily produced. The adhesion between the metal substrate acting as
the electrode support and the active material layer is generally
weak so that the active material is liable to peel off from the
metal substrate in an application using the electrode for
batteries. In the case where the electrode support acts as a
current collector, the electrical resistance of the electrode
increases thereby causing a reduced discharge voltage and discharge
capacity. In order to solve this problem, adding a great amount of
binder to the active material layer suppresses the separation. The
resultant reduced reactivity of the active material, however, has
an adverse effect on the discharge characteristic.
In a method for strengthening the adhesion between the metal
substrate and the active material layer, a thermoplastic resin
layer functioning as a binder is formed on the surface of the metal
substrate. Then, the active material is coated on the thermoplastic
resin layer and the electrode is heated, to improve the adhesion
between the metal substrate and the active material layer. This
method, however, has a disadvantage that an insulating layer is
formed between the metal substrate and the active material layer
with the result that the current collecting characteristic of the
electrode is reduced, thereby reducing the reactivity of the
electrode.
As described above, these problems are difficult to solve when a
comparatively flat metal substrate is used as an electrode
support.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide
all improvement in a coated-type electrode with an active material
layer coated on a metal substrate having a plurality of holes, in
order to achieve an improved adhesion and improved electronic
conductivity between the active material layer and the metal
substrate.
Another object of the present invention is to provide an improved
electrode for a storage battery, such as a hydrogen storage alloy
electrode using a hydrogen storage alloy powder, a nickel
electrode, a zinc electrode or a cadmium electrode.
The present invention provides an electrode for a storage battery,
comprising a metal substrate and a coated layer including an active
material and provided on at least one face of the metal substrate,
wherein the metal substrate is a metal sheet having a plurality of
punched holes with punching burrs on at least one face of the metal
sheet and along the periphery of each punched hole, and an apparent
thickness of the metal sheet including the punching burrs is at
least twice as large as the original thickness of the metal
sheet.
The present invention also provides an electrode for a storage
battery, comprising a metal substrate and a coated layer including
an active material and provided on both faces of the metal
substrate, wherein the metal substrate is a metal sheet having a
plurality of punched holes with punching burrs on both faces of the
metal sheet and along the peripheries of the punched holes, and an
apparent thickness of the metal sheet including the punching burrs
is at least twice the original thickness of the metal sheet.
The present invention also provides an electrode for a storage
battery, comprising first and second metal layers, each metal layer
having a plurality of punched holes with punching burrs on one face
of the metal layer and along the peripheries of the punched holes,
wherein an apparent thickness of each metal layer including the
punching burrs of the metal layer is at least twice as large as the
original thickness of the metal layer; and a filling of an active
material being provided between the first and second metal layers
with the punching burrs of the first and second metal layers, the
punching burrs being embedded in the active material.
Further, the present invention provides a method for producing an
electrode for a storage battery, comprising the steps of punching a
plurality of holes in a metal sheet so as to produce punching burrs
on at least one face of the metal sheet and along the peripheries
of the punched holes, and so as to produce an apparent thickness of
the metal sheet of at least twice the original thickness of the
metal sheet; producing a coated substrate by coating a paste
containing an active material on both faces of the metal sheet with
the coated substrate having a thickness of one to 1.5 times the
apparent thickness; and drying the coated substrate and compressing
the coated substrate in the direction of the thickness thereof.
According to a further aspect of the present invention, there is
provided a method for producing an electrode for a storage battery,
comprising the steps of punching a plurality of holes in a metal
sheet so as to produce punching burrs on one face of the metal
sheet and along the peripheries of the punched holes, and so as to
produce an apparent thickness of the metal sheet of at least twice
the original thickness of the metal sheet; producing a coated
substrate by coating a paste containing an active material on the
one face of the metal sheet with the coated substrate having a
thickness of one to 1.5 times the apparent thickness; drying the
coated substrate; folding the coated substrate with the coated face
being folded inwards; and compressing the coated substrate.
With an electrode of the present invention, in comparison with an
electrode which uses a two-dimensional electrode support like a
conventionally punched metal substrate, peeling off of the active
material layer from the electrode support is suppressed. At the
same time, the fact that the metal substrate has a
three-dimensional structure improves the electronic conductivity in
the direction of the thickness of the electrode. As a result, the
utilization of the active material of the electrode is improved for
a higher capacity of the electrode, thereby preventing the voltage
from dropping with a large current discharge. Further, the cycle
life is improved.
The electrode may be configured so that the active electrode
material is coated over the burrs on one surface of the metal
substrate, and the coated substrate is folded with the coated
surface being folded over onto itself. Due to this configuration,
battery characteristics equivalent to those for the conventional
sintered electrode or the foamed metal electrode are obtained,
thereby reducing the electrode cost.
While novel features of the invention are set forth in the
preceding, the invention, both as to organization and content, can
be further understood and appreciated, along with other objects and
features thereof, from the following detailed description and
examples when taken in conjunction with the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal sectional view showing an example of a
mold for producing a porous metal substrate used in an embodiment
of the present invention.
FIG. 2 is a longitudinal sectional view showing a porous metal
substrate according to an embodiment of the present invention.
FIG. 3 is a longitudinal sectional view showing a porous metal
substrate according to another embodiment of the present
invention.
FIG. 4 is a top plan view of a conventional punched metal
substrate.
FIG. 5 is a longitudinal sectional view of an electrode according
to an embodiment of the present invention.
FIG. 6 is a longitudinal sectional view of an electrode according
to another embodiment of the present invention.
FIG. 7 is a longitudinal sectional view schematically showing a
storage battery according to an embodiment of the present
invention.
It will be recognized that some or all of the Figures are schematic
representations for purposes of illustration and do not necessarily
depict the actual relative sizes or locations of the elements
shown.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following paragraphs, embodiments of the electrodes and
methods for producing the same in accordance with the present
invention will be explained in detail with reference to the
attached drawings.
FIG. 1 is a longitudinal sectional view showing a preferred
configuration of a mold used for punching holes in a metal sheet. A
male mold 5 has a multiplicity of punches 6 each having a forward
end of truncated cone shape, and a female mold 7 has recesses 8 at
positions corresponding to the punches 6.
A metal sheet (e.g. a metal plate or a metal foil) 1 is arranged
between the male mold 5 and the female mold 7. When the male and
female molds are pushed together, the metal sheet 1 is pressed into
the recesses 8 of the female mold 7 by means of the forward ends of
the punches 6 of the male mold 5. As shown in FIG. 2, the metal
sheet 1 is thus perforated to produce holes 2 while the metal
adjacent to the holes is bent out of the original plane of the
sheet 1 to form burrs 3, providing each hole with a ragged edge
extending away from a respective face of the sheet, as shown. The
holes 2 are punched, and burrs 3 are formed, by the male mold 6
pushing on the metal sheet 1 during the punching operation. The
metal sheet 1 having a thickness of t acquires an apparent
thickness T including the burrs.
FIG. 3 shows a metal substrate, in which a metal sheet 1 is punched
by use of a male mold wherein every other punch 6 is removed from
the mold shown in FIG. 1. Then, the metal sheet 1 is turned over
and is moved so that the punched holes are displaced longitudinally
by one half pitch and laterally by one half pitch. Thereafter,
punching is carried out again using the same mold. This punching
operation from the two sides produces burrs 3 on both faces of the
metal sheet 1. In the case that burrs are formed on both faces; of
a metal sheet, adjacent holes are preferably punched in opposite
directions, so that burrs are formed on opposite faces, thereby
producing a metal sheet 1 with sufficient apparent thickness T.
The metal sheet may have a thickness t of from 25 .mu.m to 100
.mu.m, and the size of the punched holes may be from 0.2 mm to 2 mm
in diameter for circular holes, and from 0.2 mm to 2 mm in the
length of each side for holes which are rectangles or similar
polygons.
The metal sheet is made of or covered with a metal which is
electrolyte-resistant.
A conventional flat punched metal for a comparative example is
shown in FIG. 4. For example, a nickel sheet 9 having a thickness
of 50 .mu.m is punched with holes 2 mm in diameter at a
center-to-center pitch (D) of 3.5 mm. The punches of the mold do
not have forward ends which are truncated cones. Instead, the metal
sheet is cut or sheared by means of the edges of the punches of the
male mold and the edges of the recesses of the female mold. The
holes thus punched are formed with very few burrs, if any, along
the peripheries thereof.
In the following paragraphs, examples of the present invention will
be described together with comparative examples by referring to the
attached drawings.
EXAMPLE 1
Nickel sheets having a thickness of 50 .mu.m were punched in
accordance with the specification shown in Table 1 thereby to
produce metal substrates. The holes are arranged in a grid with
inter-hole pitches of 3.5 mm.
TABLE 1 ______________________________________ Porous Apparent
metal Type of thickness Shape substrates punching (.mu.m) of
punched hole Remarks ______________________________________ a One
75 Generally b side 100 rectangular c 150 each side having a length
of 2 mm d Circle of 2 mm in diameter e Both 80 Generally Burrs of f
sides 100 rectangular adjacent holes g 200 each side project in
having a length opposite of 2 mm directions h Circle of 2 mm in
diameter i Same as for Disordered* samples e-g j Punched metal as
shown in FIG. 4 ______________________________________
*"Disordered" means that the punching burrs on both sides of the
metal sheet point in the two different directions in a random
manner.
These metal substrates were used to prepare paste-type nickel
electrodes. Cylindrical sealed nickel-cadmium storage batteries (C
size) were thus constructed.
First, 100 g of nickel hydroxide powder were mixed into a paste
form with 10 g of graphite powder, 5 g of nickel powder, 10 g of
cobalt powder, 55 g of 3 wt % aqueous solution of
carboxymethylcellulose and 5 g of 48 wt% styrene-butadiene rubber
aqueous dispersion. Each metal substrate shown in Table 1 was
passed through a bath containing this paste to coat the paste on
both faces of the metal substrate. The coated metal substrate
assembly was then passed through a stainless-steel slit to reduce
the paste coated substrate to a predetermined thickness. Then the
substrate was dried and compressed to prepare a coated-nickel
positive electrode having a thickness of from 0.63 mm to 0.65
mm.
Next, these nickel electrodes were cut into rectangles (i.e., 38
mm.times.220 mm). The theoretical capacity calculated from the
amount of nickel hydroxide contained in the electrode thus obtained
is in the range of from 2610 mAh to 2692 mAh.
Each of these nickel positive electrodes was combined with a
well-known cadmium negative electrode and a separator made of
unwoven fabric of polyamide resin to configure a cylindrical sealed
battery having a nominal capacity of 2.4 Ah. An aqueous solution of
potassium hydroxide (31 wt) dissolved with lithium hydroxide 30 g/1
was used in an amount of 6 ml. per cell as the electrolyte.
Batteries A to J using the nickel positive electrodes obtained
respectively from the metal substrates "a" to "j" shown in Table 1
were thus prepared.
The batteries constructed as described above were charged for 15
hours at 0.1 C (10-hour rate), and then left for one hour and
thereafter discharged at 0.2 C (5-hour rate) until the battery
voltage decreased to 1.0 V. Three cycles of this test were repeated
under the same conditions. Next, under similar charging conditions,
the fourth-cycle test was conducted with a discharge current of 0.5
C (2-hour rate), and the fifth-cycle test was conducted with a
discharge current of 1 C (1-hour rate), to compare the discharge
characteristics. Also, for the sixth and subsequent cycles, the
cycle life test was conducted by charging at 0.3 C for four hours
and discharging at 0.5 C until the battery voltage decreased to 1 V
to compare the structure of the nickel positive electrode and the
cycle life characteristics. The results are shown in Table 2.
TABLE 2
__________________________________________________________________________
Theoretical capacity of Utiliza- Capacity Capacity Discharge
Discharge positive tion at ratio of ratio of capacity at capacity
at Bat- electrode 3rd cycle 4th to 3rd 5th to 3rd 100th cycle 200th
cycle tery (mAh) (%) cycle (%) cycle (%) (mAh) (mAh)
__________________________________________________________________________
A 2631 91.1 76.2 61.2 1843 1177 B 2648 93.8 92.1 80.3 2319 1995 C
2684 95.8 95.4 89.8 2543 2388 D 2612 96.1 96.1 90.1 2487 2399 E
2669 91.8 79.3 68.0 1952 1370 F 2683 96.8 93.7 90.1 2394 2081 G
2692 99.9 99.1 93.2 2610 2493 H 2610 99.4 99.3 92.9 2575 2471 I
2650 98.8 99.4 93.0 2594 2491 J 2637 87.8 74.3 58.4 1013 242
__________________________________________________________________________
There was no conspicuous difference between the storage batteries
in the utilization of the nickel hydroxide used for the nickel
electrode. It is seen, however, that the utilization is lowest for
the battery J using the conventional flat punched metal as an
electrode support. The utilization means the ratio of the actual
capacity to the theoretical capacity. The batteries B to D and F to
I in accordance with the embodiments of the present invention, on
the other hand, are seen to exhibit superior characteristics. Also,
a great difference was observed in the high-rate discharge
characteristics, especially in the discharge capacity at 1C
discharge of the fifth cycle.
This has the following explanation. In the case in accordance with
the present invention wherein a metal sheet is processed into a
metal substrate with a three-dimensional structure having burrs
along the periphery of the holes and the apparent thickness of the
substrate including the burrs is increased to at least twice that
of the original metal sheet, the electronic conductivity in the
direction of the thickness is adequate and the capacity drop caused
by a large-current discharge is reduced.
With regard to the batteries A and E using a metal substrate having
an apparent thickness less than twice that of the unprocessed metal
sheet, by contrast, the high-rate discharge characteristic is not
as good as for batteries B to D and F to I. This indicates that the
characteristic improvement is minor for an apparent thickness of
less than twice that of the unprocessed metal sheet. Further, the
result of a cycle life test shows that the electrode in accordance
with the present invention is superior. The comparative example
(the battery J) considerably decreased in discharge capacity. A
post-test disassembly of the battery revealed that the active
material layer of the electrode was separated from the metal
substrate and this separation was a main cause of the decrease in
discharge capacity.
It can be said from the above-mentioned result that in the case
where a metal sheet punched with holes and formed intentionally
with burrs is used as an electrode support making up a nickel
electrode for a storage battery, the electronic conductivity of the
electrode is improved while at the same time suppressing separation
of the active material layer. A battery structure having a superior
discharge characteristic and cycle life characteristic can thus be
obtained. Although the holes punched from one side of the metal
sheet are effective to some degree, punching holes from both sides
is more advantageous from the viewpoint of battery characteristics
since the metal substrate is situated at the center of the
electrode. In the case where the punched holes are small, the
apparent thickness of the substrate increases by only a small
amount in comparison with the original metal sheet, and therefore
the effect of the present invention is small. When the hole size is
increased, by contrast, the pitch between adjacent holes has to be
increased, thereby resulting in a smaller contribution to an
improved electronic conductivity while at the same time reducing
the grip on the active material of the electrode. It was found that
the effect of the present invention is greatest with circular holes
having a diameter of 0.2 to 2 mm and rectangular or similar holes
having the length of each side in the range of 0.2 to 2 mm.
As described above, with the present invention, in comparison with
flat punched metal used as an electrode support of a nickel
electrode for a storage battery, the battery characteristic is
improved. Further, the electrode according to the present invention
can be produced at lower cost than those electrodes with a
three-dimensionally foamed porous nickel substrate or fabric-type
nickel processed into felt. The electrode cost can thus be reduced.
Furthermore, the present invention is obviously applicable not only
to the nickel electrode for a storage battery described above with
reference to the embodiments but also to other similar electrodes
for a storage battery including a zinc electrode, a cadmium
electrode and a hydrogen storage electrode made of a hydrogen
storage alloy powder.
EXAMPLE 2
Using a method similar to that in Example 1, a metal sheet was
punched so as to form holes with burrs from both sides to prepare a
metal substrate having a plurality of punched holes with punching
burrs on both faces thereof along the peripheries of the punched
holes. The adjacent holes of the resultant metal substrate had the
burrs on opposite faces. A paste similar to that used in Example 1
was coated on this metal substrate. The substrate was then dried
and compressed to produce a coated nickel positive electrode. Slit
widths of 1.0, 1.25, 1.5, 1.75 and 2.0 times as large as the
apparent thickness of the metal substrate were used for adjusting
the thickness after coating on of the paste.
A cylindrical sealed battery was fabricated as in Example 1 using
each electrode obtained as mentioned above, and the battery
characteristics were compared in similar fashion. As a result, the
range of slit widths in which the technical advantage of the
present invention is conspicuously observed was found to be 1 to
1.5 times the apparent thickness of the metal substrate. For the
slit width larger than 1.5 times the apparent thickness of the
metal substrate, a sufficient electronic conductivity was difficult
to secure in the direction of the thickness, resulting in a great
decrease in the battery characteristics. An appropriate apparent
thickness of the metal substrate can thus be calculated from the
slit width.
EXAMPLE 3
A method similar to that in Example 1 was used to punch holes from
one side of a nickel sheet having a thickness of 50 .mu.m, thus
preparing a metal substrate intentionally formed with burrs to
provide an apparent thickness of 150 .mu.m. In this way, a coated
nickel positive electrode was obtained. In the process, an active
electrode material was formed selectively on the surface formed
with burrs. The resultant electrode is shown in the sectional view
of FIG. 5. As shown in FIG. 6, this electrode was folded with the
active electrode material layer 4 inside, and compressed to produce
an electrode in such a form as if two electrode plates are overlaid
one on the other. A rectangular battery having a capacity of 100 Ah
shown in FIG. 7 was constructed using this electrode and a
well-known cadmium electrode. The separator and the electrolyte
were prepared using the same material as in Example 1.
In FIG. 7, numeral 11 designates the cadmium negative electrode,
numeral 12 the nickel positive electrode, numeral 13 a separator,
numeral 14 a battery casing, numeral 15 a negative terminal,
numeral 16 a positive terminal, numeral 17 a safety vent, and
numeral 18 the lid of the battery casing.
For the purpose of comparison, two similar batteries were
constructed using as the nickel positive electrode a sintered
nickel electrode and a nickel electrode with a foamed nickel porous
substrate filled with an active electrode material. The
characteristics of these batteries were compared. The three types
of battery exhibited similar battery characteristics without any
difference in performance. Thus the present invention may be used
to manufacture a battery of equivalent quality to the conventional
batteries but at a lower cost.
Although the present invention has been described in terms of the
presently preferred embodiments, it is to be understood that such
disclosure is not to be interpreted as limiting. Various
alterations and modifications will no doubt become apparent to
those skilled in the art to which the present invention pertains,
after having read the above disclosure. Accordingly, it is intended
that the appended claims be interpreted as covering all alterations
and modifications as fall within the true spirit and scope of the
invention.
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